1. Field of the Invention
The present invention relates to an improvement in a camera having a special photography function provided with at least two photographic modes: a normal photography mode and a special photography mode (soft-focus photography mode).
2. Description of the Related Art
In general photography, it is common practice to execute exposure on the basis of an appropriate exposure control value when the focus position of a photographic optical system coincides with an in-focus position. However, to diversify photographic representation, a variety of proposals have been made as to a technique for creating a special photography effect. Soft-focus photography is known as a typical technique for creating a special photography effect which is remarkably effective in taking a portrait photograph, a still-life photograph or the like.
The soft-focus photography is classified into two major categories. One category is to utilize a filter designed for soft-focus photography, and the other category is to utilize a lens designed for soft-focus photography. The filter designed for soft-focus photography, which is utilized in the former category, is a skylight filter coated with fat and oil such as a petroleum jelly, a filter having fine projections or recesses over its surface, or the like, and, in practical use, such a filter is attached to the front of a photographic lens unit. The lens designed for soft-focus photography, which is utilized in the latter category, is a photographic optical system designed to use a high-order spherical aberration to generate a light flare around the periphery of a subject image, so that an illusory effect is created.
Recently, a novel lens unit based on a sophisticated design technique utilizing a computer has been disclosed in, for example, U.S. Pat. No. 4,781,446. In normal use, the lens unit serves as an optical system free from aberration similarly to a general lens unit. However, the lens unit can also serve as a soft-focus optical system capable of generating a high-order spherical aberration by causing at least one lens in the optical system to move along the optical axis.
In addition to the above-described soft-focus photography methods, a method is known in which an ordinary camera and an ordinary lens unit are used to achieve soft-focus photography. One example of the method utilizes multiple exposure photography which is the photographic technique of exposing the same frame of film to both a focused subject image and a defocused subject image.
However, any of the aforesaid soft-focus photography methods has a number of problems. For example, in the case of the method utilizing a skylight filter coated with fat and oil, such as a petroleum jelly, which is attached to the front of a photographic lens unit, a photographer must take care of maintenance of such a filter and carry it together with a camera system at any time. In addition, the photographer is forced to perform filter replacement, according to whether a soft-focus effect is needed. Accordingly, the method utilizing the skylight filter is unsuitable for a casual snapshot which is typically made outdoors. For a similar reason, the method utilizing a filter having fine projections or recesses over its surface, which is attached to the front of a photographic lens unit, is also inconvenient if normal photography and soft-focus photography are to be selectively performed for each individual scene.
In respect of the above-described points, it seems that the lens unit which is switchable between a normal photography setting and a soft-focus photography setting soft is far more convenient than any of the aforesaid filters. This is because such lens unit eliminates the necessity of carrying a special tool or of performing a complication replacement operation and permits normal photography and soft-focus photography t be instantaneously switched. However, the use of the lens unit remarkably impairs a distinctive feature of a single-reflex camera, i.e., the advantage that various interchangeable lenses are usable. In addition, since a high-order spherical aberration is utilized, a soft-focus effect appears only when a diaphragm is set to a position equivalent to or near to an fully open aperture. As a result, it is impossible to achieve a satisfactory soft-focus effect in a place, such as the outdoors, where a subject luminance is so high that it is necessary to stop down the diaphragm to a substantial extent.
A method capable of overcoming the above-described various disadvantages is the soft-focus photography utilizing the aforementioned multiple exposure photography. However, the soft-focus photography utilizing the multiple exposure photography has the following problems.
A first problem resides in the complexity of a camera operation. More specifically, the photographer first sets a multiple exposure photography mode, and then determines exposure values for use in individual cycles of exposure to be executed in multiple exposure photography, on the basis of a measured-light value, so that a desired multiple exposure effect can be obtained, and must apply an exposure compensation to each exposure cycle on the basis of the determined exposure values. In addition, to create an optimum soft-focus effect, the photographer must take account of numerous items such as the amount of defocus by which a photographic lens is to be defocused for defocused photography, the distribution of the amount of exposure for in-focus photography and the amount of exposure for the defocused photography, and the number of cycles of exposure for the defocused photography.
If the amount of defocus in each cycle of exposure for defocused photography is extremely small, no substantial soft-focus effect can be obtained. If such an amount is extremely large, the contour line of a defocused image substantially disappears and a soft-focus effect does not appear. If a subject different from a main subject is present in a focus position reached by the photographic lens which is driven for the purpose of defocused photography, the different subject is focused and a picture partially devoid of a soft-focus effect is photographed. For this reason, the photographer must take care of the direction in which the photographic lens is to be driven for the defocused photography.
In addition, to prevent an image shake, it is necessary to extremely promptly perform an operation which follows the completion of a first cycle of exposure in the multiple exposure photography (i.e., the operation of starting a second cycle of exposure).
As described above, to successfully perform photography having a soft-focus effect by using the multiple exposure photography, the photographer must have rich experience, special knowledge or photographic knacks. The above-described camera operation is, therefore, difficult for a beginner to carry out.